SMB110

Preliminary Information

Summit Microelectronics, Inc

2099 2.3 3/1/2005

24

MINIMUM LOAD

The duty cycle is limited to a 10-90% range.

Consequently, the boost channels require a minimum

load to prevent over voltage conditions from occurring.

This may be overcome by attaching a resistor preload

to the output that matches the minimum load

requirements. This approach will result in a constant

current consumption while the outputs are enabled.

Alternatively, a zener diode (with a higher breakdown

voltage than the output) can be connected across the

output clamping the output voltage. This approach will

not draw current when the load is enabled on the

output.

MARGINING

The SMB110 has two additional voltage settings for

channels 0-3, margin high and margin low. The margin

high and margin low voltage settings have the same

voltage range as the controllers’ nominal output

voltage.

These settings are stored in the configuration

registers and are loaded into the voltage setting by

margin commands issued via the I

The margin command registers contain two bits for

each channel that decode the commands to margin

high, margin low, or control to the nominal setting.

Therefore, any combination of margin high, margin low,

and nominal control is allowed in the margining mode.

Once the SMB110 receives the command to margin the

supply voltages, it begins adjusting the supply voltages

to move toward the desired setting. When all channels

are at their voltage setting, a bit is set in the margin

status registers.

Note: Configuration writes or reads of registers

should not be performed while margining.

A typical application utilizing the margining functionality

is depicted in Figure 8. When used with a boost

controller setup as a constant current white LED driver,

margining can be used to adjust the current through the

LED chain as an adjustable brightness control.

Figure 8 – Boost configured as a constant current white LED driver with adjustable current capabilities.

SMB110

BOOST

VIN

PCHSEQ

LSDRV

COMP1(0-1.0V)

COMP2

APPLICATIONS INFORMATION (CONTINUED)